Usamos el dispositivo asegurador en la escalada en polea.

Because Spanish often drops the subject pronoun when it is clear from the verb ending.

• usamos already tells you the subject is we
• so nosotros is usually unnecessary

Both are possible:

• Usamos el dispositivo asegurador...
• Nosotros usamos el dispositivo asegurador...

The version without nosotros is more natural unless you want emphasis, contrast, or clarity.

For example:

• Nosotros usamos este dispositivo, pero ellos usan otro.

There, nosotros is useful because it contrasts with ellos.

Spanish uses the definite article much more often than English.

Here, el dispositivo asegurador means something like:

• the belay device
• or the safety device

Even when English might say we use a belay device or just we use belay devices, Spanish often prefers el when speaking generally about a tool, object, or category in context.

So el dispositivo asegurador sounds normal in Spanish.

In climbing, asegurar means to belay or to secure the climber with the rope.

So asegurador here means something related to belaying or securing. In context, dispositivo asegurador means a belay device.

A learner might notice that outside climbing, asegurador could also mean insurer or one who insures, but in this sentence the climbing meaning is the important one.

Because in Spanish, adjectives often come after the noun, especially when they describe the type or category of something.

So:

• dispositivo asegurador = belay device / securing device

This is more standard than putting the adjective first. In Spanish, the noun usually comes first, and the adjective follows it when it is classifying the noun.

Spanish often uses the definite article with general activities, subjects, and abstract nouns.

So:

• la escalada = climbing as an activity

This is normal Spanish usage. English often leaves out the, but Spanish often keeps it.

Compare:

• Me gusta la música. = I like music.
• La escalada es divertida. = Climbing is fun.

So en la escalada en polea sounds natural.

Because the two en phrases do different jobs.

1. en la escalada...
   This means in or in the context of climbing.

2. ...escalada en polea
   This is a set expression describing a specific type of climbing.

So the sentence structure is roughly:

• We use the belay device in top-rope climbing.

The repetition may feel strange to an English speaker, but it is not unusual in Spanish.

It refers to a type of climbing where the rope runs from the climber up through an anchor and back down, which in English is usually called top-rope climbing.

Literally, polea means pulley, so the phrase may look odd if translated word for word. In climbing vocabulary, though, it refers to that rope setup rather than to a literal everyday pulley in the mechanical sense.

Depending on region or climbing community, you may also hear other terms, but in this sentence the intended meaning is clearly top-rope climbing.

Yes, in some contexts para could also work, but it changes the nuance a little.

• Usamos el dispositivo asegurador en la escalada en polea.
  = We use the belay device in top-rope climbing / when doing top-rope climbing.

• Usamos el dispositivo asegurador para la escalada en polea.
  = We use the belay device for top-rope climbing.

Both can make sense.
En focuses more on the context or activity itself.
Para focuses more on purpose or intended use.

It is the present tense, but like the English present, it can express more than one idea.

Here it could mean:

• we use
• we generally use
• we use as a rule
• we are using, in some contexts, though that is less likely here

In a sentence like this, it usually sounds like a general statement or an instructional statement, not something happening only right now.

It is understandable, but in climbing Spanish there may be other ways to say it that sound more specific or more idiomatic, depending on the speaker.

For example, people might also say things like:

• Usamos el aparato asegurador...
• Usamos un dispositivo de aseguramiento...

These alternatives can sound more technical or more common depending on the context.

Still, grammatically, Usamos el dispositivo asegurador en la escalada en polea is perfectly workable and clear.

Spanish often has two ways to express this kind of idea:

1. noun + adjective

   • dispositivo asegurador

2. noun + de + noun

   • dispositivo de aseguramiento

Both are possible. The first is a bit more compact; the second can sound more technical or descriptive.

English speakers often expect of-phrases because English often says things like device for belaying or safety device, but Spanish can do this very naturally with an adjective after the noun.